1. Field of the Invention
The present invention is directed to a method and catalyst system for producing aromatic carbonates and, more specifically, to a method and catalyst system for producing diaryl carbonates through the carbonylation of aromatic hydroxy compounds.
2. Discussion of Related Art
Aromatic carbonates find utility, inter alia, as intermediates in the preparation of polycarbonates. For example, a popular method of polycarbonate preparation is the melt transesterification of aromatic carbonates with bisphenols. This method has been shown to be environmentally superior to previously used methods which employed phosgene, a toxic gas, as a reagent and chlorinated aliphatic hydrocarbons, such as methylene chloride, as solvents.
Various methods for preparing aromatic carbonate monomers have been previously described in the literature and/or utilized by industry. A method that has enjoyed substantial popularity in the literature involves the direct carbonylation of aromatic hydroxy compounds with carbon monoxide and oxygen. In general, practitioners have found that the carbonylation reaction requires a rather complex catalyst system. For example, in U.S. Pat. No. 4,187,242, which is assigned to the assignee of the present invention, Chalk reports that a carbonylation catalyst system should contain a Group VIII B metal, such as ruthenium, rhodium, palladium, osmium, iridium, platinum, or a complex thereof. Further refinements to the carbonylation reaction include the identification of organic co-catalysts, such as terpyridines, phenanthrolines, quinolines and isoquinolines in U.S. Pat. No. 5,284,964 and the use of certain halide compounds, such as quaternary ammonium or phosphonium halides in U.S. Pat. No. 5,399,734, both patents also being assigned to the assignee of the present invention.
The economics of the carbonylation process are strongly dependent, inter alia, on the number of moles of aromatic carbonate produced per mole of Group VIII B metal utilized (i.e. xe2x80x9ccatalyst turnoverxe2x80x9d). Consequently, much work has been directed to the identification of efficacious inorganic co-catalysts that increase catalyst turnover. In U.S. Pat. No. 5,231,210, which is also assigned to General Electric Company, Joyce et al. report the use of a cobalt pentadentate complex as an inorganic co-catalyst (xe2x80x9cIOCCxe2x80x9d). In U.S. Pat. No. 5,498,789, Takagi et al. report the use of lead as an IOCC. In U.S. Pat. No. 5,543,547, Iwane et al. report the use of trivalent cerium as an IOCC. In U.S. Pat. No. 5,726,340, Takagi et al. report the use of lead and cobalt as a binary IOCC system.
Further complexity was added to carbonylation catalyst systems by Buysch et al. in U.S. Pat. No. 5,502,232, which ostensibly teaches the use of a quaternary salt, a cocatalyst, a base, and a desiccant in a supported Pd-based carbonylation system. In U.S. Pat. No. 5,821,377, Buysch et al. report the use of said aforementioned catalyst system with the Pd and the cocatalyst provided on the same support.
The literature is virtually silent, however, as to the role of various catalyst system components, such as IOCCs and onium halides for example, in the carbonylation reaction (i.e., the reaction mechanism). Accordingly, meaningful guidance regarding the identification of additional catalyst systems is cursory at best. It would be desirable to identify catalyst systems that would minimize consumption of costly components (e.g., palladium and onium halides) or perhaps that would omit these components. It would also be desirable to minimize the aforementioned consumption of costly components while increasing selectivity toward desirable products and minimizing formation of undesirable byproducts (e.g., 2- and 4-bromophenols). Unfortunately, due to the lack of guidance in the literature, the identification of effective carbonylation catalyst systems has become a serendipitous exercise.
As the demand for high performance plastics continues to grow, new and improved methods of providing product more economically are needed to supply the market. In this context, various processes and catalyst systems are constantly being evaluated; however, the identities of improved and/or additional effective catalyst systems for these processes continue to elude the industry. Consequently, a long felt, yet unsatisfied need exists for new and improved methods and catalyst systems for producing aromatic carbonates and the like.
Accordingly, the present invention is directed to a method and catalyst system for producing aromatic carbonates. In one embodiment, the present invention provides a method of carbonylating aromatic hydroxy compounds by contacting at least one aromatic hydroxy compound with oxygen and carbon monoxide in the presence of a carbonylation catalyst system that includes an effective amount of a Group VIII B metal source; an effective amount of a bromide composition; an effective amount of an activating organic solvent; an effective amount of a combination of inorganic co-catalysts comprising a lead source and a copper source; and an effective amount of a base.
In various alternative embodiments, the carbonylation catalyst system can include an effective amount of a palladium source and an effective amount of an alkaline metal bromide salt. Further alternative embodiments can include an effective amount of a polyether.